Homogenization is the breaking down and mixing of the components of an emulsion or dispersion. A major use of homogenizers is to break down and disperse milk fat into the bulk of skim milk. This delays creaming of milk fat globules. Homogenizers are also used to process other emulsions such as silicone oil and to process dispersions such as pigments, antacids, and various paper coatings.
In the most widely used type of homogenizer, the emulsion is introduced at high pressure of from 500 psi to 10,000 psi (34.5 to 689.5 bar) to a central bore within an annular valve seat. The emulsion is forced out through a narrow gap between the valve seat and a valve member. Through the gap, the emulsion undergoes extremely rapid acceleration as well as an extreme drop in pressure. This violent action through the valve breaks down globules within the emulsion to produce the homogenized product.
The degree of homogenization is a function of the difference between the pressure of the emulsion at the inlet to the valve and the pressure at the outlet. Past systems for homogenizing milk have, for example, used an inlet pressure in the order of 2,000 psi (137.9 bar). To improve the final product, two stage systems have been used. In such systems, liquid from a high pressure pump delivers liquid to the gap of a first homogenizing valve, and the liquid which is thus homogenized is directed to a second valve through which the liquid is expressed for further homogenization. The total pressure of the system is the sum of the pressure drops across the two valves.
Recently, in an effort to reduce the amount of energy required to homogenize milk and other products to a predetermined degree, attempts have been made to decrease the required homogenizing pressure.